Superradiance in massive vector fields with spatially varying mass

Superradiance is a process by which massive bosonic particles can extract energy from spinning

black holes, leading to the build up of a “cloud” in cases where the particle has a Compton wavelength

comparable to the black hole’s Schwarzschild radius. Previous works have studied how spatial

variations in the metric and interactions with other fields can lead to the mechanism being enhanced,

or stalling, in more realistic cases. One particularly interesting case is that of superradiance occurring

for photons in a diffuse plasma, where they gain a small effective mass. Studies of the spin-0 case

by Dima et al. have indicated that such a build up is suppressed by a spatially varying effective

mass, in cases where this is supposed to mimic the photons’ interaction with a physically realistic

plasma density profile. We repeat these studies using relativistic simulations of a massive Proca

field on a Kerr background, which allow us to treat the spin-1 case directly relevant to photons. We

track and measure the superradiant growth in a time evolution, finding similar qualitative results

to the scalar case, and so supporting the conclusions of that work. Simulations of this type only

provide a toy model of the interaction of the bosons with a plasma-like fluid, so we suggest several

ways to extend our simulations to treat more realistic scenarios.